1. Field of the Invention
The present invention relates to an AC (alternating current) motor control apparatus and specifically to a position-sensorless motor control method and apparatus that estimates and detects a magnetic pole position of a synchronous motor""s rotor without needing a sensor thereby controlling the AC motor.
2. Description of Prior Art
Patent document 1: Japanese Application Patent Laid-open Publication No. Hei 07-245981; and
Patent document 2: Japanese Application Patent Laid-open Publication No. Hei 08-149898.
To achieve highly responsive control of the speed or torque of a synchronous motor, technologies disclosed in those documents adopt vector controls that perform coordinate transformation of the motor current both in the magnetic flux direction (magnetic pole position direction, d-axis) and in the direction (q-axis) perpendicular to the magnetic flux direction based on the magnetic pole position of the motor""s rotor. Since the control requires a sensor to detect a magnetic pole position, a magnetic pole position sensor is a requisite. However, recently, a variety of xe2x80x9cmagnetic pole position-sensorless control systemsxe2x80x9d have been developed to control a synchronous motor by detecting a magnetic pole position without using a position sensor.
In general, synchronous motors can be classified into two types: cylindrical types and salient-pole types (Ldxe2x89xa0Lq; Ld denotes inductance in the d-axis direction and Lq denotes inductance in the q-axis direction). Among them, a salient-pole synchronous motor""s magnetic pole position estimation method includes a method that uses voltage induced by the motor and a method that uses the motor""s salient-pole property.
For example, the prior art includes the patent document 1. This publication discloses a rotor position detection system that applies an alternating current voltage to a motor and separates the generated motor current into the parallel component direction and the perpendicular component direction to the alternating current voltage thereby detecting the rotor position based on the motor current components of at least one direction.
The prior art also includes the patent document 2. A primary winding""s leakage inductance changes by influence of magnetic saturation in the teeth. Therefore, the technology disclosed in this document superimposes an alternating current voltage other than the fundamental wave component, measures the inductance of the winding based on the relation between the current""s flow and the alternating current voltage, and then estimates magnetic flux from the inductance fluctuation. This documents describes the control of an inverter""s output voltage and current according to the estimated magnetic flux.
The above prior art is theoretical based on the motor""s salient-pole characteristic and provides an effective system that can accurately estimate a magnetic pole position by inputting the motor current.
The above prior art uses the characteristic that when an alternating current voltage is applied to a salient-pole motor, a current is also generated in the direction perpendicular to the alternating current voltage application vector when the application vector is not parallel to or perpendicular to the magnetic flux direction (d-axis). Therefore, by using the above characteristic, it is possible to estimate and detect the rotor position (magnetic pole position) using the salient-pole property in the area where motor current is relatively light and does not cause magnetic saturation.
However, in a heavy current area where motor current causes local magnetic saturation minimizing the inductance in the motor current direction, even when the application vector is parallel to or perpendicular to the magnetic flux direction (d-axis), a current also flows in the direction perpendicular to the alternating current voltage application vector. As a result, it may become impossible to estimate the position of the rotor by using the salient-pole property.
In view of the above, an object of the present invention is to provide a motor control method and apparatus which has a position estimation means that can accurately and reliably estimate the rotor position even when local magnetic saturation occurs in the motor current direction due to heavy current.
The above-mentioned problems can be solved by the following means:
A position-sensorless motor control method of controlling a PWM inverter for applying voltage to a salient-pole AC motor and controlling the AC motor, wherein vector control of the AC motor is performed by detecting motor inductance in the pre-determined direction to the detected current vector direction of the AC motor and estimating the AC motor""s rotor position based on the detected motor inductance.
Further, the above-mentioned method applies voltage in the pre-determined direction to the AC motor""s current vector direction to detect the rotor position, detects the current fluctuation condition caused by the applied voltage, detects inductance based on the detected current fluctuation condition, estimates and detects the AC motor""s rotor position by using the detected inductance, thereby performing vector control of the AC motor.
Furthermore, the controller detects inductance in the direction perpendicular to the AC motor""s current vector direction within the range determined in terms of detection accuracy of the motor""s rotor position, estimates and detects the AC motor""s rotor position based on the detected inductance, thereby performing vector control of the AC motor.
Moreover, the above-mentioned method applies voltage in the pre-determined direction to the AC motor""s current vector direction to detect the rotor position, detects the current fluctuation condition caused by the applied voltage, calculates inductance based on the detected current fluctuation condition, estimates and detects the AC motor""s rotor position, thereby performing vector control of the AC motor.
Furthermore, the above-mentioned method estimates and detects the AC motor""s rotor position based on the difference between the detected current fluctuation condition and the reference current fluctuation condition calculated from the torque command and rotation speed, thereby performing vector control of the AC motor.
Moreover, this method is a position-sensorless motor control method wherein the pre-determined direction to the AC motor""s current vector direction is the direction perpendicular to the current vector direction.
Furthermore, a motor control apparatus comprising a PWM inverter for applying voltage to a salient-pole AC motor and a controller for controlling the PWM inverter, wherein the controller comprises a means for applying a position detection voltage signal in the pre-determined direction to the AC motor""s detected current vector direction and detecting the current fluctuation condition caused by the position detection voltage, a means for detecting the motor inductance from the detected current fluctuation, and a position estimation means for estimating the AC motor""s rotor position based on the detected motor inductance, thereby performing vector control of the AC motor.
Further, the above-mentioned apparatus comprises a position estimation means for estimating and detecting the AC motor""s rotor position based on the detected motor inductance and the reference inductance determined by the torque command and motor speed.
Further, the pre-determined direction is the direction perpendicular to the current vector direction.
Furthermore, the above-mentioned apparatus comprises a position estimation means for estimating the AC motor""s rotor position based on the difference between the current fluctuation condition caused by the position detection voltage and the reference current fluctuation condition calculated from the torque command and rotation speed.
Moreover, the above-mentioned apparatus corrects the reference current fluctuation condition according to the magnitude of the input voltage of the PWM inverter.
Furthermore, the above-mentioned apparatus corrects the reference current fluctuation condition according to the operating point of the AC motor.
Moreover, the above-mentioned apparatus makes the reference current fluctuation condition into a table for each operating point of the AC motor or a table according to the magnitude of the PWM inverter""s input voltage and stores the table in the controller.
Further, a motor control apparatus comprising a PWM inverter for applying voltage to a salient-pole AC motor and a controller for controlling the PWM inverter, wherein the controller comprises a position estimation means for detecting motor inductance in the direction 45 degrees to the magnetic flux axis and estimating the AC motor""s rotor position based on the detected motor inductance.
Furthermore, the above-mentioned apparatus comprises a position estimation means for estimating the AC motor""s rotor position based on the current fluctuation condition detected by applying a position detection voltage signal in the direction 45 degrees to the magnetic flux axis.
Moreover, the above-mentioned apparatus comprises a position estimation means for estimating the AC motor""s rotor position based on the difference between the detected current fluctuation condition and the reference current fluctuation condition.